Surgery is characterized by a continuous search towards minimal invasiveness. Since the 1980s open surgery has been largely replaced by an endoscopic approach in which long instruments are inserted through trocars in a carbon dioxide-extended abdomen. Laparoscopic surgery, known for its validated benefits of shorter hospitalization, less postoperative pain and earlier recovery, is more demanding for the surgeon. Precise dissection, suturing and knot tying in minimal access surgery is an advanced skill. Especially when the suture line and the axis of the needle holder are unparallel this skill is difficult to master. Recent steps in the evolution towards minimal invasiveness are Single Port Surgery (SPS) and Natural Orifice Transluminal Endoscopic Surgery (NOTES). Both approaches result in a scarless healing. In SPS the instruments are inserted through one big trocar through e.g. the umbillicus.
A disadvantage of endoscopic surgery is reduced dexterity for the surgeon. This is mainly because of the fulcrum effect and the absence of wrist like movements at the tip of the instrument. Awareness of this disadvantage increases as more complex endoscopic procedures and single port surgeries (characterized by sword fighting of the instruments) are performed.
The fulcrum effect is explained by the long instruments that pivot at the level of the trocar inserted in the abdomen. A movement of the handle to the left is translated in a movement to the right at the effector (e.g. a pair of scissors). It is surprising to see how quickly a surgeon can adapt to these inversed movements.
The lack of wrist-like movements is more difficult to overcome. A state-of-the-art solution is provided by the surgical robot. In this master slave system the movements of the surgeon's hands at the console are transferred to fluent movements at the instrument's tip. This solution is quite expensive, leading to the development of cheaper hand instruments with an omni-directional articulated tip
Most of the challenge is explained by the reduced dexterity. A conventional rigid laparoscopic instrument offers only 4 degrees of freedom (rotation, up/down angulations, left/right angulations, in/out movements).
To overcome this restriction in movements, various designs for steerable instruments have been developed. In its simplest form an articulated instruments consist of a prebent flexible tube sliding out of a rigid straight tube (uni-directional articulated instruments). This tip can only bend in one direction and cannot withstand an appropriate amount of lateral force. More advanced alternatives are instruments that allow bending movements of the tip in one plane. Because of the nature of the construction, a mostly stable tip is created. These bi-directional instruments need to be navigated to a point of interest by bending into one direction and then by turning the whole instrument around its own axis. This is not intuitive. True wrist movements are only possible with omni-directional systems. The omnidirectional articulated instruments consist mainly of a proximal and distal end, a proximal and distal bending part and an intermediate portion in between. Movement of the proximal end is transferred to a movement at the distal end. Examples are described in U.S. Pat. Nos. 7,410,483 and 8,105,350.
Similar to robotic surgery, omni-directional articulated instruments provide 7 degrees of freedom (axial rotation and deflection of the tip in two planes are added to the 4 DOF of conventional rigid instruments). A combination of up/down and left/right movements at the proximal side allows to reach any point at the distal effector side without the need for a rotation around its own axis.
The increased manoeuvrability is paid back by a serious decrease in tip stability. To solve this, hybrid solutions such as the Kymerax® system (Terumo) and Jaimy® system (EndoControl) compensate by using strong electrical motors to restore the tip stability.
Omni-directional articulated instruments offer, in comparison to robotic systems the advantages of low costs and tactile feedback.
A problem in the art of omni-directional articulated instruments is in the assembly thereof. The steering wires are required to be narrow so as to be able to maximise the number of wires which leads to a smoother steering. Threading thin wires into a steerable tube housing may present a problems of pushability since the thin wire is prone to buckling, and the problem of friction increases the further the wire is inserted into the tube. With a steerable tube of 30 cm of more in length, insertion of each wire by this method is time consuming. An alternative problem is how to assemble a robust steerable tube, particularly where the end of the steering wires need to be secured around an annular ring to provide push/pulling forces to the wires. Welding the ends to the annular ring can produce weaknesses, is time consuming, and leads to an increased diameter of the instrument. The use of adhesive relies on a strong bond between the elements; the forces exerted and daily instrument use can cause one of more wires to slidably detach from the annular ring. A pre-attached annular ring is impossible to thread into an instrument. The present invention provides a solution to one or more of these problems.